Suppression of superconductivity by magnetic field in quench-condensed ultrathin films of indium

Abstract

Current-voltage characteristics and magnetoresistance are measured in an ultrathin film of indium with a mean-field transition temperature T c0 =4.3 K . They show similar power-law behaviors of the forms V ∞ I a and R ∞ B b . The results are explained in terms of vortex unbinding by a current and a magnetic field, implying that the superconducting transition is of the Kosterlitz-Thouless type. A magnetic field is also used to tune a thinner film with T c0 ≈ 3.9 K through the superconductor-insulator transition. The temperature- and magnetic-field-dependent resistance obeys the scaling function proposed by Fisher with a critical exponent z B V B ≈ 0.5 , which is somewhat smaller than has been predicted.